Cleanup and consolidate unused CSS code

My site is 10 yrs old, we have added new CSS code from time to time and have added more than one css files. I want to cleanup unused code and consolidate into one single file for faster downloading. If there is a technique to cache the CSS so it is not downloading every time a page is called, then great, that skill will be considered in the bid. One website with two domains - [[login to view URL]][1] and [[login to view URL]][2] - use same css files, it is ok to combine all in one. I am guessing, one can produce the new cleaned up css files without having ftp access to the site? If not access can be given but it will be done on live site, our test site is too outdated :)